I think I have the clinical tone down, but the narration may be a little wishy-washy. I'm also not quite sure about the level of detail (less can be more, and I certainly didn't use less), as well as how interesting the idea is in general (Safe SCP's can be a hit or miss).
Thanks!

The following suggestions in relation to the above excerpt may be contradictory, but they are equally valid:

Capitalize the "F" in Foundation.

Get rid of the phrase "Foundation-tested" entirely — it's a fireproof safe, simple as that. And given that the anomaly's effects are limited to its interior, I'd actually consider placing the thing in a plain, old "standard secure locker" rather than shell out the extra effort to get a fireproof safe.

…which may be left unlockedis to be locked at all times except during approved testing.

I don't think the Foundation would have been so careless as to ever have allowed this anomaly to remain in an unlocked container, even before it was proven potentially lethal.

Also, it can really be assumed and not mentioned that an anomaly should be locked up at all times outside of approved testing.

Due to instances of unapproved testing, SCP-XXXX's containment room is to be fitted with one (1) CCTV camera with a two-day recording backlog.

My biggest issue with this is that "unapproved testing" actually occurred.

Besides that, surveillance is another one of those things that can be assumed to already exist for every anomaly.

While cross-linking is promoted nowadays, cross-linking to Series I is seen as something of a cheap shot. If you're going to keep the note, I highly recommend losing the reference to the infinite pizza box.

… any food items coming in contact with SCP-XXXX are only to be handled or consumed by Class D expendable personnel.

While D-class personnel are indeed expendable, the SCP community tends to regard such neglectful treatment of hard-to-come-by human resources negatively. It makes sense to only let D-class handle the contaminated food, but I doubt the Foundation would let them eat it.

Check out the guide Containment Protocols for some more detailed explanation of what can go unsaid when writing this section of an SCP article and how to make special containment procedures actually "special" as opposed to standard.

Description:

…the interior of SCP-XXXX remains at an unknown temperature tested to be in excess of 106 Kelvin.

It seems to me that if they know the temperature is "in excess of 106 Kelvin", then it's not entirely "unknown".

Pieces of SCP-XXXX-01, when broken, pull apart into fibers extremely similar to asbestos insulation.

Instead of saying the fibers are "extremely similar to asbestos insulation", I would opt to say the fibers are "greatly resembling asbestos."

…at which point it resumes its main anomalous property.

Perhaps try "primary" in place of "main". It sounds somewhat more scientific, and you get a bit of nice alliteration with "property".

…concentrations as small as .05 ppm, if ingested, have been found to induce instant tumorous growths through the body.

Quite the notable anomalous effect you have here! I'm surprised you don't add a little more information in the description about this.

Other:

Note: Due to the informative nature of many of the following incidents, they have been listed within the same numeration as approved experiments. Incidents are designated as I-XXXX-XX and Experiments as E-XXXX-XX.

This note shouldn't have to be included. A reader is able to figure out the information provided as they go.

Note: Shit. They're gonna kill me.
- Leonard

It breaks my suspension of disbelief that this line would make it into an incident report.

Note: Good thing I assumed that stuff was just asbestos and didn't touch it. Shame about Dr. Namira — he was a great drinking buddy. Better get some clearance on storing this thing from now on.
- Leonard

The problem I see here is that there always should have been security clearance and classification on this anomaly.

Although I've nit-picked at tone and execution in the critique above, I gotta say that I like the concept you have in this article. It's simple, it's fodder for some amusing moments, and it's exactly the kind of mostly-harmless anomaly the Foundation would have buried in a facility somewhere. I hope to eventually see a future version on the mainlist.

Be sure to come back to this forum for feedback on your next draft of this article!